Electro-static photo-copier machine

Abstract

The copying machine of the present invention is capable of executing a reversal image forming mode wherein a toner is only deposited onto a non-image portion of the latent image to visualize. When the reversal image forming mode is designated, a screen member, which is movable to intrude into or extrude from the light path of the exposing means, is controlled to intrude into the light path of the exposing means to form a reversal image.

What is claimed is: 
     
       1. A copying apparatus comprising: first charging means for charging an electrostatic latent image bearing member to a predetermined potential;   exposing means for scanning an original document in a predetermined direction for exposing the document to the charged electrostatic latent image bearing member to form an electostatic latent image;   a screen member having a pattern of light blocking portions thereon and movable into and out of the light path between the exposing means and said image bearing member;   second charging means for recharging the electrostatic latent iamge formed on the electrostatic latent image bearing member, said second charging means having a grid;   developing means for developing the electrostatic latent image formed on the electrostatic latent image bearing member;   first mode designating means for designating a reversal image forming mode wherein a toner is deposited only onto a non-image portion of the latent image;   first control means to which said first mode designating means is connected and connected to said screen member for causing the screen member to move into the light path when the reversal image forming mode is designated by the first mode designating means; and   second control means to which said first mode designating means is connected and connected to said second charging means for operating the second charging means when the reversal image forming mode is designated by the first mode designating means.   
     
     
       2. A copying apparatus as claimed in claim 1 wherein the pattern on said screen member has opaque colored lines formed on a transparent substrate and extending perpendicular to the scanning direction of the exposing means. 
     
     
       3. A copying apparatus as claimed in claim 1 wherein the pattern on said screen member has opaque colored mesh dots. 
     
     
       4. A copying apparatus as claimed in claim 2 further comprising means for supplying said grid with a voltage which is substantially lower than the surface potential at an image portion of the latent image and slightly higher than the surface potential at a non-image portion of the latent image and having a polarity the same as the polarity of the first charging means. 
     
     
       5. A copying apparatus as claimed in claim 4 wherein the developing means comprises means normally developing the electrostatic latent image with a toner charged to a polarity opposite to that of the first charging means. 
     
     
       6. A copying apparatus as claimed in claim 5 wherein the copying apparatus further comprises second mode designating means for designating an outline image forming mode wherein toner is deposited only on an outline portion of the latent image. 
     
     
       7. A copying apparatus as claimed in claim 6 wherein said second mode designating means is connected to said first control means and said first control means comprises means to control said screen member to withdraw said screen member from the light path when the outline image forming mode is designated by the second mode designating means. 
     
     
       8. A copying apparatus as claimed in claim 7 wherein the second control means comprises means for operating said second charging means when the outline image forming mode is designated by the second mode designating means. 
     
     
       9. A copying apparatus as claimed in claim 1 wherein the pattern on said screen member has lines which are capable of reflecting light formed on a transparent substrate and extending perpendicular to the scanning direction of the exposing means. 
     
     
       10. A copying apparatus as claimed in claim 1 wherein the pattern on said screen member has mesh dots capable of reflecting light. 
     
     
       11. A copying apparatus as claimed in claim 9 further comprising means for supplying said grid with a voltage which is substantially higher than the surface potential at an image portion of the latent image and slightly lower than the surface potential at a non-image portion of the latent image and having a polarity the same as the polarity of the first charging means. 
     
     
       12. A copying apparatus as claimed in claim 11 wherein the developing means comprises means for reversely developing the electrostatic latent image with a toner charged to a polarity the same as that of the first charging means. 
     
     
       13. A copying apparatus as claimed in claim 12 wherein the copying apparatus further comprises second mode designating means for designating an outline image forming mode wherein toner is deposited only on an outline portion of the latent image. 
     
     
       14. A copying apparatus as claimed in claim 13 wherein said second mode designating means is connected to said first control means and said first control means comprises means to control said screen member to withdraw said screen member from the light path when the outline image forming mode is designated by the second mode designating means. 
     
     
       15. A copying apparatus as claimed in claim 14 wherein the second control means comprises means for operating said second charging means when the outline image forming mode is designated by the second mode designating means. 
     
     
       16. A copying apparatus comprising: first charging means for charging an electrostatic latent image bearing member to a predetermined potential;   exposing means for scanning a positive original document in a predetermined direction for exposing the document to the charged electrostatic latent image bearing member to form an electrostatic latent image;   a screen member having a pattern of opaque portions thereon and movable into and out of the light path between the exposing means and said image bearing member;   second charging means for recharging the electrostatic latent image formed on the electrostatic latent image bearing member, said second charging means having a grid and means to apply a voltage to said grid which is substantially lower than the surface potential at an image portion of the latent image and slightly higher than the surface potential at a non-image portion of the latent image and having a polarity the same as the polarity of the first charging means;   developing means for normally developing the electrostatic latent image formed on the electrostatic latent image bearing member with toner charged to a polarity opposite to that of the first charging means;   first mode designating means for designating a reversal image forming mode wherein a toner is deposited only onto a non-image portion of the latent image;   first control means to which said first mode designating means is connected and connected to said screen member for causing the screen member to move into the light path when the reversal image forming mode is designated by the first mode designating means; and   second control means to which said first mode designating means is connected and connected to said second charging means for operating the second charging means when the reversal image forming mode is designated by the first mode designating means.   
     
     
       17. A copying apparatus as claimed in claim 16 wherein the pattern on said screen member is lines formed perpendicular to the scanning direction of the exposing means. 
     
     
       18. A copying apparatus comprising: first charging means for charging an electrostatic latent image bearing member to a predetermined potential;   exposing means for scanning a negative original document in a predetermined direction for exposing the document to the charged electrostatic latent image bearing member to form an electrostatic latent image;   a screen member having a pattern of light reflecting portions thereon and movable into and out of the light path between the exposing means and said image bearing member;   second charging means for recharging the electrostatic latent image formed on the electrostatic latent image bearing member, said second charging means having a grid and means to apply a voltage to said grid which is substantially higher than the surface potential at an image portion of the latent image and slightly lower than the surface potential at a non-image portion of the latent image and having a polarity the same as the polarity of the first charging means;   developing means for normally developing the electrostatic latent image formed on the electrostatic latent image bearing member with toner charged to a polarity the same as that of the first charging means;   first mode designating means for designating a reversal image forming mode wherein a toner is deposited only onto a non-image portion of the latent image;   first control means to which said first mode designating means is connected and connected to said screen member for causing the screen member to move into the light path when the reversal image forming mode is designated by the first mode designating means; and   second control means to which said first mode designating means is connected and connected to said second charging means for operating the second charging means when the reversal image forming mode is designated by the first mode designating means.   
     
     
       19. A copying apparatus as claimed in claim 18 wherein the pattern on said screen member is lines formed perpendicular to the scanning direction of the exposing means.